1. Field of the Invention
The present invention is directed to a method for manufacturing micromechanical sensors, particularly absolute pressure sensors, that are preferably manufactured in the framework of a CMOS process and are arranged on a substrate as a micromechanical component.
2. Description of the Related Art
Capacitative pressure sensors are utilized for measuring absolute pressure. A closed chamber having a reference pressure is terminated by an elastic membrane that is exposed to an external pressure. The electrically conductive membrane, together with the side of this chamber that lies opposite, forms a plate capacitor. The membrane is deformed due to the pressure difference between the external pressure and the internal reference pressure. The capacitance of this capacitor changes due to the changed distance between the membrane and the backside of the chamber acting as a cooperating electrode that, for example, can be formed by a doped region produced in semiconductor material. The external pressure can be identified from this change in capacitance. Such an arrangement is disclosed, for example, by U.S. Pat. No. 5,095,401. One problem in the manufacture of such pressure sensors in the framework of a CMOS process derives in that, after the cavity provided under the membrane has been etched out, this cavity must be closed and the closure layer provided therefor is applied at a pressure of more than 10 mbar. The gas enclosed in the cavity therefore has too high a pressure, this having a negative influence on the sensitivity and temperature stability of the sensor. The relatively dense gas in the cavity heats too greatly given existing membrane oscillations and thereby falsifies the measured result. A corresponding difficulty occurs given encapsulated acceleration sensors wherein a moveable micromechanical mass part is arranged in a cavity that is closed off from the outside.